Journey to the centre of the earth, Part 2

Before I dive into the main topic of today’s blog, I’ve got a request!

We’d like your help to improve the RSPB's online information for anyone wanting to make their gardens, balconies and local greenspace better for wildlife.

It would be in the form of a chat with my lovely colleague Adam Walker or one of his team.

If you think you could can spare some time, please email adam.walker@rspb.org.uk and he will get back to you with further details so you can work out a suitable time to speak.

It doesn’t matter if you have used the RSPB website or not, nor the size of your garden, your age, where you live, or indeed how much you have done in your gardens. Whoever, whatever – we'd love you to help us get it right.

I hope to hear that loads of you take up the invitation!

Right, back to the garden. Two weeks ago I did an initial blog about soil, and how important it is, and how it is predominantly made up of tiny fragments of rock and mineral, rather than being pure organic material.

That last fact then helps explain a number of things:

• Why pots of compost and raised beds can drop so much in level over time. Yes, their contents settle down, but mostly they decompose, which of course bits of rock don’t.
• Why you should shake soil off weed roots before they go on the compost heap. The bits of rock don't help all that fast decomposition you're after.
• Why a turf stack (lumps of turf layered upside down) is different to a compost heap. The mix of rock and organic matter slowly turns into beautiful soil to put back on the garden.

In the previous blog also promised a second way of learning more about the soil in your garden. It is the ‘Shake it all About’ method, and here's me doing it. 

• Get a glass jar with a lid.
• Fill it about a third full with a sample of soil from about 6-10 inches (15-25cm) down in your earth.

• Fill the jar to two thirds full with tap water.
• Then shake vigorously. For about three minutes. The first minute will be easy; by the third you'll feel like you've had a complete workout. It will make you appreciate so much more anyone who plays the maracas. The result will probably look like chocolate milkshake (but I can confirm it doesn't taste like it).

• Then let it settle.

Any sand should drop out in the first minute.

Any silt should drop out in the next five minutes.

Clay particles can take anything from a day to two whole-long weeks to drop out. (I advise that you go and do something else rather than watch this happen).

And large organic particles should float on top.

Here's mine after two days - can you see the beautiful layers? Gritty at the bottom, dark silt in the middle and paler clay at the top (with more clay still to drop out of the murky water).

You can then estimate the relative proportions of the different layers in your soil, which in mine are about 30% sand, 60% silt and 10% clay.

You can then read across this clever little diagram to work out what your soil is (follow the angle of the numbers to choose the right lines):

Mine, it says, is a silt loam.

What this doesn't do is tell you what pH your soil is - whether it is acid or alkaline, which is also good to know. I'm not a fan of the cheap home test kits which, in my experience, give really ropey results. Much better is to see what is already growing in your garden or those around you.

If there are lots of heathers, camellias, rhododendrons, Scots Pine and Japanese maples, then you're very likely to be on acid soils. Your soil is also likely to be sandy or peaty.

If there plenty of ash trees and whitebeam, and shrubs such as lilac, juniper and ceanothus grow well, then you are likely to be on alkaline soil, most typically over limestone or chalk.

And all this in turn will greatly affect the communities of wildlife that live there. The soil determines the plants which determine all sorts of things such as the types of butterfly and moth you are likely to find.

So I'll leave you today with a photo from my garden this week of Silver Birch trees, which like my slightly acid soil, as seen through the burnt umber leaves of my Wild Service Tree, which likes the clay content in my soil.

And of course all this autumn colour will then drop and decompose and add to the wonderful treasure that is our soil.